(a) Field of the Invention
The present invention relates to the technical field of the continuous casting of molten metal.
(b) Description of Related Art
A device for holding and replacing plates or tubes for transferring molten metal contained in a metallurgical vessel is already known in the art. The device can be arranged immediately below a metallurgical vessel and is used for transferring the molten metal from an upper metallurgical vessel to a lower metallurgical vessel for instance from a ladle to a tundish or from a tundish to a casting mould.
The plate generally consists of a metallic casing surrounding or cladding a refractory material. The plate is used to transfer the molten metal, either in the form of a free flow, or through a tube rigidly connected to the plate. In the latter case, the plate is frequently referred to as a “casting tube”, “outer nozzle”, submerged nozzle or pouring nozzle. Hereinafter, the term plate will be used to refer both to the plate for transferring molten metal in free flow form and to the plate provided with a tube referred to as a casting tube.
The devices for holding and replacing plates or tubes may have different names on the market such as tube changer device, device for the insertion and/or removal of a pouring nozzle, calibrated nozzle changer, tube exchange device or others.
A device for holding and replacing a plate for casting molten metal out of a vessel generally comprises a frame with a casting opening, said frame being configured for being fixed to the lower side of a metal casting vessel and comprising a first, upper portion and a second, lower portion, joining at a middle section plane defining the plane where an upper refractory element and a lower refractory element form a sliding contact,                the upper side portion of the frame comprising n upper refractory element receiver, or means for receiving and clamping in place at its pouring position the upper refractory element, such that the through bore of the upper refractory element is in fluid communication with the casting opening and        the lower side portion of the frame comprising:        a passage extending along a first axis of first direction (X) between an inlet opening and an outlet opening configured for receiving and moving a plate from said inlet to said outlet, passing by a casting position in registry with the casting opening of the frame;        a displacing element, or means for displacing, and a guide, or means for guiding, the plate from a standby position to a casting position in registry with the casting opening of the frame, and optionally for guiding it to the outlet, said guide or guiding means running substantially parallel to the first direction (X),        substantially parallel to the first direction (X) and extending from the guide or guiding means at the level of the pouring nozzle casting position, means for pressing up the plate at its casting position in the direction of the upper portion of the frame (in the direction of the metallurgical vessel).        
More specifically, the device generally consists of a frame comprising two guiding rails and rockers arms or thrusters for cooperation with a plate or a plate of a casting tube. The means for displacing the plate generally consist of a mechanical, pneumatic or hydraulic arm or cylinder.
The frame of the device for holding and replacing a plate is generally cast and is unlikely subjected to wear. However, the parts such as the clamping means, the guiding means and the thrusting means like the clamps, the rails, the rockers or the springs are wearing parts of the device. These parts are checked at each maintenance operation of the device and replaced if necessary.
The plate arranged below the vessel is worn in the course of metal casting, for example due to slag erosion. The casting orifice may also become clogged or obstructed over time. It is thus necessary to replace the plate during casting, using a device for holding and replacing the plate. Such devices are known particularly from the document EP 0 192 019 A1 relating to a device for replacing casting tubes and the document U.S. Pat. No. 6,019,258 relating to a device for replacing calibrated plates. The plate is replaced in the casting position by sliding a new plate which was in standby forwards, said new plate pushing the worn plate, so as to eject and replace said plate in the casting position. The devices generally comprise guiding means such as rails or slides and thrusting means or pushing means such as springs. The guiding and displacing means are used to guide and move the plate to the operating position thereof or remove the same from the operating position thereof. The thrusting or pushing means are used to hold the plate in tight contact with the refractory element located upstream when the plate is in the operating position.
Providing a sealing surface or shut-off surface or blank surface on the plate, arranged behind the plate casting orifice is known from the document WO 20041065041. This sealing surface is intended to seal the casting channel of the metallurgical vessel if required, for example in the event of an accident. Indeed, it may be necessary to stop (interrupt) the metal casting in the event of an emergency. For this purpose, it is simply necessary to push (move forward) the plate in the casting position by a distance greater than or equal to the casting channel diameter, so that the sealing surface blocks (closes) the channel.
In a device for holding and replacing a plate suitable to interrupt the cast in case of an emergency, the displacing means can adopt two successive positions:                a casting position wherein the plate is in fluid communication with the casting channel        a sealing position wherein the sealing surface of the plate is facing the casting channel        
Such devices generally require the use of a so-called double stroke jack or cylinder, the short stroke displacing the plate to the casting position and the long stroke displacing the plate to the sealing position. The sealing position is also called shut-off position or closure position.
By convention, the forward direction of a plate, frame or device for replacing plates is defined with reference to the direction of plate replacement in the device for replacing plates, the plate being moved forwards to adopt the following successive positions: standby position, casting position (when the casting orifice extends from the casting channel), sealing position (when the sealing surface seals the casting channel) and ejection (evacuation or exit) position (when the casting plate is released from the device).
One difficulty lies in that it is possible to arrange a new plate by mistake in the wrong direction in the device for holding and replacing plates. In this case, the sealing surface is not arranged behind but in front of the casting orifice. As a result, when the new plate is pushed to the casting position, the casting orifice thereof does not extend exactly from the casting channel and, furthermore, if the new plate is then pushed to the sealing position in the event of an emergency, the sealing surface is not opposite the casting channel, such that the casting is not completely discontinued. This may have serious consequences for the metal casting facility and for those working on the casting site, in that it is no longer possible to discontinue the casting.
FIG. 1 represents an example wherein a plate 10 according to the prior art has been inserted the wrong direction in a device 90 for holding and replacing plates. The device is used for transferring molten metal in a continuous casting facility, for example steel, for example from a tundish to a casting mould. The plate 10 replaces a worn plate 12, by sliding the plate 10 in the direction 14 corresponding to the first translation axis X, under the thrust of the displacing means, for example a hydraulic cylinder. In FIG. 1, the plate 10 is in a position which should have been a casting position if it had been inserted in the right direction.
The plate 10 comprises a sliding face 16, in contact with an upstream refractory element, with reference the direction of molten metal flow corresponding to the axis Z. More specifically, the face 16 is in contact with an inner nozzle 18 of the vessel, arranged in the bottom of the vessel, said inner nozzle 18 comprising a casting channel 20.
The sliding face 16 comprises a casting orifice 22, intended to extend from the channel 20 when the plate 10 is arranged in the right direction in the casting position, and a sealing (shut-off) surface 24, for sealing (closing) the channel 20 when the plate moves to the sealing (shut-off) position.
As can be seen in FIG. 1, when the plate 10 is in the casting position and in the wrong direction, only one gap 26 is generated between the casting channel 20 and the casting orifice 22. Therefore, although a maximum molten metal flow rate would be required, only the gap 26 allows the molten metal to pass through. Furthermore, if, for exceptional reasons, it is desired to discontinue casting, by pushing the plate 10 to the sealing position, the gap 26 widens and the casting channel 20 is not sealed by the sealing surface 24 allowing molten metal to pass through. This gap may even be the cause of leakage liable to allow the metal to infiltrate the device for replacing plates, and cause non-negligible damage in the casting facility.
The aim of the present invention is particularly that of improving the safety in the continuous casting facility in a simple manner.
The fact that an operator can arrange a plate in the wrong direction has been discussed in the documents U.S. Pat. No. 5,211,857 or U.S. Pat. No. 5,011,050. The devices described in these documents present two directions perpendicular to one another. One plate insertion direction or loading direction and one plate replacement direction or firing direction. The loading direction is perpendicular to the plate exchange direction. The plate exchange direction is parallel to the casting mould. The insertion of the plate into the device is made by sliding it onto the loading rails. The safety system comprises a pre-position guide defining a gauging opening therethrough complementary to the plate to require a single plate orientation to pass through said gauging opening as the plate is loaded into the device. In the loading area, the loading rails are asymmetrical or present a locating step which in cooperation with the pre-position guide prevent the plate from reaching the loading position if the plate orientation is not correct. In particular, the above documents describe a device having two different loading rails. For instance, one of the rails has a projection engaging with a groove arranged on the plate sliding surface. In the plate replacement direction, the two edges of the plate are identical and are devoid of asymmetry. This way, the core part of the device which operates the plate replacement is not modified internally and is substantially identical to the other known devices.
The devices describe in the documents U.S. Pat. No. 5,211,857 or U.S. Pat. No. 5,011,050 involve certain drawbacks. They require the use of a pre-position guide unit and the proper mounting of this last. The projection, the groove or the locating step have to be properly mounted on one of the loading rails. Furthermore, the projections and grooves have relatively small dimensions. It is thus possible that the operator would not realise that the plate has been arranged in the wrong direction. The rails are worn over time and the projections are also worn; it is possible that, after a certain period of use, the projection no longer fulfils the role thereof. The rails are also wearing parts requiring regular replacement. During the assembly or the maintenance of the device, the operator could easily make a mistake during the mounting of the loading rails and/or the pre-guide unit. For instance, he could position the left rail on the right or vice versa or forget to add the locating step.